Roadside bombs are commonly used by Taliban insurgents to target Afghan and foreign forces but often cause civilian casualties.

Attacks that kill civilians usually go unclaimed and there was no immediate admission of responsibility for the deaths.

On Saturday, Afghan MPs have summoned top security officials about security during an upcoming election run-off. Defence minister Bismillah Mohammadi said army forces were ready to handle security for the run-off, which will happen on June 14th.

"The enemies of Afghanistan have increased their attacks recently, because we are going to the elections run-off, and they want to cause this process to fail," Mohammadi added. "But they will fail".

Afghanistan is in the middle of presidential elections, with former foreign minister Abdullah Abdullah and ex-World Bank economist Ashraf Ghani due to compete in a head-to-head run-off vote next month.

Both candidates have promised to bring peace after decades of conflict. But they will have to tackle a challenging security situation without NATO combat troops, all 51,000 of whom will pull out by the end of this year.

President Barack Obama on Tuesday outlined the US strategy to end America's longest war, saying that the 32,000-strong US deployment in Afghanistan would be scaled back to around 9,800 by the start of 2015.

Those forces would be halved by the end of 2015 before eventually being reduced to a normal embassy presence with a security assistance component by the end of 2016.

The US troops will stay only if a key security pact, the Bilateral Security Agreement, is signed between Kabul and Washington. The outgoing Afghan President Hamid Karzai refuses to sign the pact, but both Afghan presidential candidates have vowed to sign it if elected.